1. Field of the Invention
The present invention relates to a device for the measurement of acoustic reverberation time, and more particularly to a device employing a narrow band audible signal which can be selected by means of individual band-pass filters.
2. The Prior Art
The acoustic properties of the recording space are very important in sound recording, and particularly important is the reverberation time which is a complicated function of many factors including the volume of the recording space, and the sound absorption of the materials defining the space. The reverberation time is the time interval that extends from the time of cessation of a sound source, until the time at which the acoustic pressure resulting from such sound source has decreased to one-thousandth part of its original value, i.e., the acoustic pressure level decreases by 60 dB. It is customary to use a narrow band noise signal with a bandwidth of approximately one-third of an octave. It is known to generate such a signal by means of a noise generator, and pass the noise generator signal to a loudspeaker through a band-pass filter having a pass band of one-third octave. When the signal is turned off, the signal after cessation is recorded by way of a microphone, and again filters through a band-pass filter. It is necessary that the filter for the transmitting function and the filter for the receiving function be tuned to the same mean frequency in order to obtain significant results.